The present invention relates to tank pressure control systems, and particularly to a system which automatically develops a predetermined pressure head in a fuel tank during refueling to prevent a fuel pump operator from overfilling the fuel tank. More particularly, the present invention relates to a valve system communicating with a fuel tank venting outlet for blocking fuel vapor flow through the venting outlet to a separate filler neck coupled to the fuel tank only during refueling to develop said predetermined pressure head while otherwise venting such flow to a pressure-vacuum relief cap on the filler neck during times other than refueling.
Vehicle fuel systems are known to include pressure-relief valves mountable on either fuel tanks or filler necks. These conventional valves are not equipped to regulate the volume of fuel introduced into the vehicle fuel system during refueling. Although fuel pump nozzles are known to include sensor means for shutting off the flow of fuel from the nozzle when the fuel tank is nearly filled, it has been observed that users frequently manually override or bypass such fill-limiting sensors by continuing to pump fuel after the pump nozzle has automatically shut off several times. It will be appreciated that such unauthorized refueling practices can result in overfilling the fuel tank which can effectively reduce the fuel vapor expansion capacity available within the filled fuel tank.
An improved tank pressure control system is provided for maintaining a head pressure within the fuel tank which exceeds the maximum head pressure that can develop in the filler neck due to filling the filler neck with fuel. The improved control system advantageously aids in preventing fuel pump operators from overfilling fuel tanks by providing a pressurized fuel vapor barrier within the fuel tank that acts to block the introduction of fuel into the fuel tank in excess of a predetermined fuel capacity during refueling.
At the same time, the improved system is adapted to release fuel vapor in periods other than during refueling to increase the flow of fuel vapor to, for example, the atmosphere under the control of a pressure-relief fuel cap or the like. Such a timely release of fuel vapor from the fuel tank minimizes the risk that an excessive pressure buildup will occur in the tank during vehicle operation and drive a surge of liquid fuel through the filler neck to impinge the fuel cap and thereby avoid shortcomings of known fuel tank pressure control systems.
According to the present invention, an apparatus is provided for controlling discharge of fuel vapor from a fuel tank having a filler neck during refueling. The apparatus includes means for conducting fuel vapor between the fuel tank and a distal portion of the filler neck, means for selectively blocking flow of fuel vapor through the conducting means, and means for yieldably biasing the blocking means away from a flow-blocking position to a flow-delivery position.
The apparatus further includes means defining a venting control chamber in communication with the blocking means for using liquid fuel in the fuel tank to develop a pressure head in the venting control chamber having a magnitude in excess of a predetermined threshold level. The pressure head in the venting control chamber exerts a closing force on the blocking means in opposition to the biasing means so that the blocking means is moved from its normal flow-delivery position to its flow-blocking position. Such flow-blocking action prevents discharge of pressurized fuel vapor in the tank to the filler neck through the conducting means to aid in developing a pressure head in the fuel tank which prevents intentional or inadvertent overfilling of the tank.
In preferred embodiments, the venting control chamber is situated outside of the fuel tank and the using means further includes means extending into the fuel tank for communicating liquid fuel from the fuel tank toward the venting control chamber. In one embodiment, the communicating means is positioned outside of the conducting means, while, in another embodiment, the communicating means extends through the conducting means. In each case, the mixture of air and fuel vapor present in the venting control chamber is compressed as a result of continuing communication of more and more liquid fuel toward the venting control chamber as the volume of liquid fuel in the tank increases during refueling. Such compression raises the pressure in the venting control chamber sufficiently to impose a closure-inducing force on the blocking means in opposition to the biasing means.
Also in preferred embodiments, the fuel tank is formed to include a venting outlet separate from the filler neck. The conducting means includes a vent housing extending through the venting outlet into the fuel tank and partition means for dividing the vent housing into an inner chamber communicating with the fuel tank and an outer chamber communicating with the filler neck. A seal is established in the venting outlet between the vent housing and the fuel tank. The partition means includes a valve seat having an inner edge defining a venting aperture interconnecting the inner and outer chambers.
The blocking means includes a valve member formed to include means for sealingly engaging the valve seat to block flow of fluid through the venting aperture between the fuel tank and the filler neck. In one of the embodiments, the communicating means is formed within the vent housing itself, while in another of the embodiments the valve member is formed to include a central aperture coupled to the communicating means so that the communicating means moves in unison with the valve member and pressurized fuel vapor is communicable from the fuel tank to the venting control chamber via the communicating means.
In each embodiment, the communicating means provides a pressure transmission passage interconnecting the fuel tank and the venting control chamber in fluid communication. An inlet is formed and situated for admitting liquid fuel into the pressure transmission passage in proportion to the volume of liquid fuel in the fuel tank in excess of a first predetermined volume. As a result, the pressure in the pressure transmission passage and the venting control chamber will increase in response to continued admission of liquid fuel into the pressure transmission passage as the volume of liquid fuel in the fuel tank increases over and above the first predetermined volume.
A first outlet of the pressure transmission passage communicates pressure extant in the passage to the venting control chamber at a first predetermined rate to permit development of a pressure head in the chamber sufficient to move the blocking means against the biasing means to a flow-blocking position. A second outlet of the pressure transmission passage communicates pressure extant in the passage to the conducting means at a second predetermined rate.
A porous element is provided in the second outlet to impede the flow of liquid fuel through the second outlet means and restrict transmission of pressure from the pressure transmission passage to the conducting means. Such restriction will cause the second predetermined rate of pressure discharged through the first passage outlet to be less than the first predetermined rate of pressure discharged through the first passage outlet so that a pressure head sufficient to move the blocking means to its flow-blocking position develops in the venting control chamber. Such a movement-inducing pressure head is developed in the tank in response to accumulation of liquid fuel in excess of a second predetermined volume which is greater than the first predetermined volume.
One feature of the present invention is the provision of vent control means for using liquid fuel in the fuel tank to develop a pressure head in a venting control chamber communicating with the means for selectively blocking flow of fuel between the fuel tank and its filler neck. A steadily increasing volume of liquid fuel is admitted into a pressure transmission passage communicating with the venting control chamber as the level of liquid fuel into the tank rises above a certain threshold level during refueling. This steadily increasing volume acts to compress the mixture of air and fuel vapor in the venting control chamber, thereby causing the blocking means to move from its normal flow-delivery position to its flow-blocking position.
Advantageously, closure of the means for conducting fuel vapor from the fuel tank to the filler neck by the blocking means in accordance with this "vent control" feature establishes a trapped vapor volume in the tank above the liquid fuel level and the fluid connection point of the tank and filler neck. Such a trapped vapor volume provides a pressure barrier which acts to prevent introduction of additional liquid fuel into the tank through the filler neck, thereby preventing a fuel pump operator from inadvertently or intentionally manipulating the pump nozzle control to overfill the fuel tank.
Another feature of the present invention is the provision of the porous element in the second outlet of the pressure transmission passage to "bleed" pressure gradually from the venting control chamber to the conducting means. Although such bleeding is not significant enough to prevent development of sufficient pressure in the venting control chamber during refueling to move the blocking means to its flow-blocking position, it is significant enough, over time, to release the built-up pressure in the venting control chamber sufficiently during periods in which no liquid fuel is being dispensed into the fuel tank to enable the blocking means to be moved by the biasing means to resume its normal flow-delivery position.
This "pressure bleeding" feature advantageously permits fuel vapor in the fuel tank to be vented to the filler neck for possible subsequent distribution to the atmosphere under the control of a pressure-relief valve in a fuel cap on the filler neck unless the cap is removed and refueling is underway. Advantageously, such a tank overfill-limiting valve system does not block venting of fuel vapors from the fuel tank during periods before and after refueling. In other words, the tank venting system is in operation during all running conditions of the vehicle carrying the specially equipped fuel tank while the cap is installed in its filler neck-closing position. One benefit of such venting is that the risk of excessive pressure buildup in the fuel tank resulting in a surge of liquid fuel from the tank against the fuel cap through the filler neck during vehicle operation is minimized.
Additional objects, features, and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.